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Interval training for team sport: why rest matters
SPB looks at new research on high-intensity interval training for team sport players and the role of rest length for maximizing training benefits
In recent years, a growing body of evidence has accumulated showing that performing regular bouts of high-intensity interval training is an extremely effective training tool for athletes seeking to maximize performance for a relatively low training workload(1). Put simply, short sessions of high-intensity intervals are a great way of producing gains in aerobic power, enabling an athlete to sustain a higher intensity/pace/workload for longer before fatigue sets in. What’s less clear however is the optimum recipe of an interval program for maximizing gains.
How long, how hard?
That high-intensity interval training (HIIT) is effective is not in doubt. However, what’s much less certain about HIIT is how a session should be put together for maximum fitness gains? There are many variables to that come together when constructing an interval session. These include(2,3):
· Interval duration – how long should each work interval be?
· Intensity – how hard should each work interval be (this can be measured in terms of speed, power or heart rate)?
· Interval numbers - how many intervals should the session contain?
· Rest duration – how long should each rest period in between each work interval be?
· Rest type – active or passive
· Total interval training time per week
The short answer to the above is that we cannot actually say what the perfect recipe is. Given that each of the six variables above can be manipulated in so many ways, there are literally thousands of possible ‘recipe’ permutations, making it impossible for scientists to provide a definitive answer (so far). And even if we did know, it would likely depend on the type of event an athlete is training for.
What we can do however is identify the characteristics of interval sessions that are likely to produce good gains in fitness. And when we do that, we can use the findings from existing research demonstrating that best training effects in terms of improving fitness (ie increased stroke volume and oxygen delivery around the body), is achieved at training intensities between 85%–95% of maximum heart rate(4,5), and possibly even higher(6). In other words, designing an interval session that manages to raise heart rates to around 90% or even 95% of maximum for a reasonable period of time is likely to produce a better training effect that an interval session that does not.
HIIT and rest periods
If we now consider HIIT as a mode of interval training, we can see why it is effective; the intense nature of the intervals in a session means that an athlete performing them will experience a more rapid rise and greater increase in heart rate during each interval, which will mean a greater time proportion of each interval will be spent above 90% maximum heart rate. Of course, in very intense intervals, each interval duration will be likely be shorter than a lower-intensity interval session, so the total time accumulated above 90% maximum heart rate might not be that much greater. However, as a proportion of the total work performed, HIIT provides an excellent way of ensuring an effective training stimulus.
However, something that also becomes apparent is the effect of rest period lengths on the overall impact of a HIIT session. For any given interval duration, a shorter rest length in between intervals means less time for heart rate to fall following each interval, which in turn means that the total time accumulated above the 90% maximum heart rate threshold is increased – ie the potential benefits are increased. But of course, this is counterbalanced by less recovery time and greater accumulated fatigue. Less recovery and more fatigue inevitably mean that the number of intervals that can be completed in a session falls, and this means less total work done. If the total work performed declines too much, the training stimulus may be insufficient to reap the potential rewards of a HIIT session. In effect, interval numbers, intensity and rest length have to be balanced to give the desired outcome.
High intensity intervals for team sport
One area of sport where getting the balance between rest period length and total number of quality interval completed can be particularly tricky is team sports – for example soccer, rugby, hockey etc. These sports are characterised by high intensity bursts of activity, interspersed by lower intensity activity and stoppages in play of various lengths(7). Moreover, research shows that the ability to perform at high intensity, recover adequately between intense bursts and to repeat these maximal intensity actions for the duration of a match is a crucial quality that team players need to develop in preparation for competition(8).
Data shows that in most team sport events, most of the high-intensity bursts of activity typically last for very short periods – typically less than ten seconds’ duration with the average duration around six seconds(9). When training this ability therefore, it makes sense to focus on the phosphocreatine energy pathway in muscles. This energy pathway is very quick reacting and is where stored ATP for muscular contraction is used immediately, then regenerated.
This can happen because phosphocreatine stored in muscles can donate its phosphate to a spent ATP molecule (ADP), thereby regenerating ATP (see figure 1). The immediate use of muscle ATP only supplies about 10 seconds’ worth maximum of energy but that’s sufficiently long for the task at hand, and the used ATP (ADP) can be fully regenerated in around 60 seconds via the phosphocreatine system. This short-term energy pathway is in sharp contrast to the breakdown of carbohydrate in the absence of oxygen and the breakdown of carbohydrate and fat in the presence of oxygen to generate ATP, which you will probably know as the lactate and aerobic pathways respectively. These systems are much longer lasting, but cannot regenerate ATP at the same rate, which means exercise intensity must be reduced accordingly (see figure 2)
Figure 1: Structure of the ATP energy molecule
The sugar ribose forms part of the framework (along with adenosine) upon which the ‘action’ section of the molecule (three phosphate groups – P- ) is hung. ATP releases immediately usable energy when the very energetic bond between the two end phosphate groups (shown in pink) is broken – ie ATP breaks down to form ADP. AT can be quickly regenerated by the the donation of a phosphate from phosphocreatine stored in muscles.
Figure 2: Schematic representation of contribution over time of the body’s energy systems
Pink = ATP system; blue = CP system; green = lactate system; black = aerobic system. The ATP system supplies immediate energy for very high-intensity exercise but only lasts for around 10 seconds. It can however, be regenerated by the phosphocreatine system in under a minute.
Training the ATP/phosphocreatine system
Where the goal is to improve the capacity of team sport athletes to perform repeated high- or very high-intensity sprints, training the phosphocreatine system is a must. An effective training method to achieve this is the use of a form of HIIT known as intermittent sprint training. Intermittent sprint training (IST) is comprised of maximal intensity efforts of less than 10 seconds with longer rest periods of more than 60 seconds, allowing substantial or near complete recovery in between efforts(10). In particular, the longer rest periods used in IST increase the likelihood of maximum intensity performance being maintained for a greater number of repetitions compared to shorter rest periods(11). That’s a good thing as not only can athletes accumulate a more meaningful training load in a session, this format also more closely replicates the demands in a match situation.
There is a drawback to this approach though and that is time. Accumulating a reasonable number of sprint repeats with longer periods of rest periods in between is time consuming; for example, a single session of two sets of 8 x 8-second sprints with a rest period of three minutes in between each sprint would take at least 45 minutes. Since players also need to meet tactical, technical, psychological and other physical development goals (eg strength and endurance), this can be a logistical nightmare for coaches, who really need their player to perform time-efficient training(12).
How short can recoveries be?
Data shows that when sprint training takes place, partial recovery occurs during the first 20 or so seconds, nearly complete recovery occurs after around a minute but full recovery and replenishment of the phosphocreatine stores taking as long as three minutes(13). Since time-efficient training is a high-priority in team sport athletes, a key question is just how short can recoveries in an IST session be while still allowing athletes to accumulate a useful training load and one that is relevant to a match situation? Until recently, there was very little data on this topic, but a newly-published study on IST in rugby and netball players provides some valuable answers.
New research
Published in the ‘Journal of Exercise Science and Fitness’, this study investigated the effect of three different recovery periods on power output, calorie expenditure and perceived exertion, as well as the blood lactate response during a cycling ergometer IST trial in female national-level team sport athletes(14). In the study, 13 elite female athletes playing at national level were recruited; seven participants played rugby and six played netball. Regardless of the sport played, all the participants were undertaking a training regimen of three technical and tactical training sessions, three full-body strength sessions, and two speed and conditioning training sessions per week.
All the athletes undertook three different trials on a cycling ergometer on three separate occasions. Each trial consisted of five-minute warm up pedaling at 70rpm, with the pedaling resistance set according to manufacturer recommendations based on weight and sex. At the third, fourth and fifth minute of the warm-up, the participants completed a two-second sprint at the highest rev·min−1 they could achieve. Following three-minutes of passive recovery sitting quietly on the bike, the participants completed an IST trial consisting of 10 x repetitions of a six-second sprint. However, the three trials (performed in a random order) differed in the rest lengths between intervals:
· R60 – trial with 60 s recovery between sprints
· R90 - trial with 90 s recovery between sprints
· R120 - trial with 120 s recovery between sprints
For all sprint efforts, peak power output (PPO), mean power output (MPO), and ‘total work’ were recorded. In particular, the researchers wanted to find out how the different rest periods affected the ability of the athletes to complete a high-quality set of sprints so a measure of how performance declined through each set of sprints was also calculated. High-quality sprints were defined as those where the PPO stayed above 95% (abbreviated PPO95+). The performance decline during each set of sprints was arrived at using the following formula:
Percentage decline = 1 − (sum of sprints 1 to 10/best sprint × 10) × 100
In addition, to power outputs, measures of blood lactate and perceived exertion for each trial were also recorded.
What they found
The results were pretty clear cut. When it came to maintaining high-quality sprint performance and keeping power outs close to maximum, the longer recoveries were not only superior, they also resulted in less perceived fatigue. Taking average power output per sprint for example, the athletes managed 743 watts per sprint in the 120-second rest condition, 734 watts in the 90-second rest condition but only 710 watts per sprint in the 60-second rest condition. Despite the lower power outputs, perceived fatigue rose as rest periods became shorter; on the 6-20 Borg scale, perceived exertion was recorded at 13.9, 14.2 and 15.5 for the 120, 90 and 60-second rests respectively.
The decline in performance in terms of high quality reps was also much more evident as rest lengths shortened. Also performance declined throughout all three trials (as you would expect) the decline in performance was much more marked with the 90-second and especially the 60-second rest length. As figure 3 shows, when looking at the number of sprints completed where peak power output (PPO) was maintained above 95%, in the 60-second rest length trial, more than half of the athletes failed to maintain 95% PPO after just three sprints!
Figure 3: Decline in peak power outputs across the trials
The decline in PPO is far greater in the 60-second rest trial compared to the 120-second rest trial, with the 90-second trial being intermediate. The result is far fewer high-quality sprints being completed in the 60-second rest trial.
Practical implications for team sport athletes
Repeated sprint ability is an essential element for success at high levels of team sports, so training is matters. What this research shows is that when training the ability to carry out repeated short sprints, any interval session needs to ensure rest lengths are adequate. In the study above, the greatest number of high-quality sprints, the highest average power output per sprint and higher calorie burn were all achieved with 120-second rest intervals. Moreover, this protocol also resulted in the lowest perceived exertion!
Looking at the data above, we can also see that while the 90-second rests were not as conducive to performance as the 120-second rests, they were far more superior than the 60-second rests. In other words, while there was a drop in outcomes going from 120 to 90 seconds, this drop was modest. But the drop from 90 to 60 seconds was much greater, which suggests that if time is really tight, 90-second rests could be a useful compromise whereas 60-second rests are just too compromised for this type of training.
It’s also worth noting that the results seem to vary quite a lot from athlete to athlete. For example, in the 90-second rest trial (figure 3), one of the athletes managed to maintain 95%+ of PPO right up until the last sprint whereas three of the athletes struggled to do this right from the beginning of the trial! This suggests that coaches (and athletes) may need to experiment with sprint intervals to find what kind of compromise in terms of time/effectiveness works best for them. Some athletes may find that they can knock out a good session of high-quality sprints using just 90-second rest lengths whereas others may need 120 seconds or perhaps even up to 180 seconds to maintain session quality.
References
1. Sports. 2015 Oct;45(10):1469-81
2. Sports Med. 2002, 32, 53–73
3. J. Strength Cond. Res. 2007, 21, 188–192
4. J. Strength Cond. Res. 2013, 27, 1974–1980
5. J. Med. Sci. Sports 2013, 23, 74–83
6. Sports Med. 1986, 3, 346–356
7. Sports Med. 2017;47:2533–2551
8. PLoS One. 2017 Feb 15;12(2):e0171462
9. Scand J Med Sci Sports. 1997;7:206–213
10. Sports Med. 2011;41:673–694
11. J Hum Kinet. 2015;49:171
12. Eur J Sport Sci. 2021 May;21(5):695-704
13. Pflügers Archiv. 1976;367:137–142
14. J Exerc Sci Fit. 2024 Apr;22(2):97-102. doi: 10.1016/j.jesf.2023.12.004. Epub 2023 Dec 11
Andrew Hamilton
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